1. Field of the Invention
The present invention relates to a method of coating a plurality of layers successively on a travelling support. More particularly, the present invention relates to a method of multilayer coating suitable for use in the production of magnetic recording tape.
2. Background of the Invention
One of the recent trends in the area of magnetic recording is to use media, such as tape, that are thin and which yet are capable of high-density recording. In response to this need, the use of dual-layered magnetic coatings instead of single-layered systems is increasing. At the same time, the provision of primer coatings is common practice for the purpose of improving the adhesion between the support and the magnetic layer or back layer and this also calls for dual- or three-layered system. Presently, multi-layered coating is accomplished by repeating the coating and drying steps for individual layers. However, this method is not highly productive and requires high initial cost. It is therefore desired to develop a method that is capable of forming multiple layers in a single coating and drying zone. In this coating method which is hereunder referred to as a multiple coating method, it is at least required that the need to dry the coated layers one by one be eliminated.
The coating techniques currently employed in the production of magnetic recording media include roll coating, gravure coating, and a combination of roll coating or extrusion coating with doctor knife coating. However these methods obviously are incapable of forming multiple coatings because of the shearing force exerted during the coating operation.
Various proposals have been made with respect to the technique of extrusion coating but they all relate to the formation of single coatings. Techniques using a slide coater with slots has been proposed for providing multi-layered coatings in photographic materials. However, this method is not suitable for use in the manufacture of magnetic recording media because the coating solutions employed in their production are dispersions in organic solvents that are highly viscous, easy to agglomerate and dry, and are not adapted to high-speed coating.